Minimally Invasive Replacement Of The Pulmonary Valve: Histological Effects Of Non-orthotropical Placement Of The Valve Carrying Stent
Dominik Richter, Saskia Pokorny, Irma Haben, Anja Metzner, Jessica Haupt, Georg Lutter.
Herz- und Gefäßchirurgie USKH Kiel, Kiel, Germany.
OBJECTIVE: The minimal invasive replacement of heart valves more and more enters daily clinical practice. The experimental percutaneous, transluminal replacement of the pulmonary valve with tissue enginieered heart valves carried in a nitinol-stent is focus of our recent research. Due to the size of the stent and the fact, that the position of a once placed stent is not correctable, the position may be non-orthotropic. This study explores the consequences of such an incorrect positioning.
METHODS: In this study ten pulmonary valved stents were implanted in sheep - five were placed correctly and in the remaining five cases the stent was in a non-orthotropic position after placement. After 3-6 months the animals were sacrificed and the histologic architecture and amount of collagen was analyzed and evaluated using the Movat pentachrome, van Gieson and immunhistochemical staining of collagen I and III. With the aid of native valves, a classification for the amount of collagen, cell wealth and development of the architecture of the valves was defined.
RESULTS: The layering, the core architecture of the valves were in both groups identical and were therefore not modified because of the non-orthotopic position. However, the content of collagen III, the most important structure protein in the heart valve, was higher than in the valves that were placed correctly. In addition to that, the count of cells was much higher than in the valves that were placed non-orthotropically.
CONCLUSIONS: At first, the tissue engineered heart valves seem to develop in their layering in a normal way even if the conditions are not ideal. But the underdevelepment of collagen III and the higher amount of cells, as we see it in hyperplasic or inflammated tissues, seem to be a result of the incorrect placement of the valve. The incorrect placement of a valve-carrying stent therefore has not only haemodynamic effects, but the development of the histological structure of the valve is effected as well. In conclusion, the correct positioning of the stent is very important for the outcome of the replacement and should be improved to guarantee a good outcome of our future patients.
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